Project Summary Opioid use disorder (OUD), dependence on prescription opioids and heroin, is a major public health problem taking a devastating toll on Americans, their families, and their communities. Three million Americans have or have had OUD. Opioid overdose deaths have quadrupled in the United Sates since 1999 (33,000 in 2015). Buprenorphine/naloxone (BUP), a partial opioid agonist combined with an antagonist, is a well-established outpatient treatment for OUD that can only be prescribed by appropriately trained physicians. Patients with untreated OUD often seek medical care in emergency departments (EDs). ED-initiated BUP doubles the rate of engagement in addiction treatment in ED patients with OUD. However, the practice of initiating BUP in the ED has not been implemented into ED care. Poor health information technology (HIT) usability is a major challenge to implementation of evidence-based medicine. To improve the HIT user experience and uptake of evidence-based medicine, HIT interventions should be developed using user-centered design. We propose a multicenter, pragmatic, stepped wedge implementation trial to evaluate the effect of user-centered computerized clinical decision support (CDS) for ED patients with OUD upon rates of ED-initiated BUP and referral for ongoing medication assisted treatment (MAT). The aims for the UG3 Planning Phase (Year 1) are: (1) Develop a pragmatic, user-centered CDS for ED-initiated BUP and referral for MAT in ED patients with OUD which will automatically identify and facilitate management of potentially eligible patients and (2) Establish the infrastructure for the proposed trial. In the UH3 Phase (Years 2-5) we will execute the trial with the specific aim to: Compare the effectiveness of user-centered CDS for BUP to usual care on outcomes in ED patients with OUD. We will test the primary implementation hypothesis that rates of ED-initiated BUP are higher with user-centered CDS. This trial will be pragmatic and offer advantages over more actively collected and distal outcomes by: (1) evaluating the effects of an intervention under the usual conditions in which it will be applied, (2) utilizing structured data from the EHR that can be passively collected, and (3) requiring no specific expertise or training of clinicians. Formative process evaluation, incremental cost effectiveness, and return on investment analyses will be performed to optimize the context for implementation of the user- centered CDS into routine ED practice and to evaluate its value. Given BUP's dramatic effect on engagement in treatment, this trial will answer the critical implementation question in OUD care: ?What is the best way to maximize the rate of adoption of ED-initiated BUP and referral to MAT? Our findings will have immediate and lasting impact upon individuals with OUD. Our collaborative network between Yale, the Mayo Clinic, and UNC is poised to efficiently carry out a trial of this design and magnitude. The study will be spearheaded by leading experts in ED-initiated treatment in substance abuse, user-centered health IT, and data management.